Solid propellant grain of variable electron-emissive composition



M C. HUGHES TAL PRO NT RAI F VARIA CTRON-EMISSI Filed Jan SOLID PELLA ELE Juy 20, 1965 E N O VE COMPOSITIO 22, 1962 FIG.

FIG.2

INVENTORS MARTIN 0. HUGHES THOMAS K. HILLAR AGENT United States Patent O 3,195,392 StlLiD PRPELLANT GRARN @E VARIABLE ELECTRN-EMHSSIVE CMPOSITN Martin C. Hughes, Faits Church, and Thomas K. Miilar,

Springield, Va., assignors to Atlantic Research Corporation, Fairfax County, Va., a corporation of Virginia Filed Jan. 22, 1962, Ser. No. 167,686 14 Claims. (Cl. dii-35.6)

This invention relates to and has as its principal object the provision of an electron and ion generator designed to produce by chemical means an ionized atmosphere in the form of a s-tream of electrons and ions modulated in emission density ina contnolled, pre-scheduled manner.

The need for such an ionized gas generator has arisen for a variety of reasons. it can be employed, for example, to reproduce artificially certain upper atmosphere ionized conditions for laboratory study of ytheir effect on such phenomena as transmission of electromagnetic signals, such as radio or television broadcasts which normally travel through atmospheric regions of varying electrical field intensity.

It has recently been shown by prior investigations that inorganic alkali metal oxidizer salts react With finelydivided metals of lower oxidation potential to produce the free alkali metal in ionized state and free electrons.

FIGURE l is a diagramma-tic longitudinal section through a rocket motor illustrating the features of the invention.

FGURE 2 is a cross-sectional view taken on lines 2-2 of FIGURE l.

Broadly speaking, the invention comprises fabricating a shaped, solid grain which varies incrementally in electron-emissive composition in a direction normal to at least one initial burning surface of the grain and seating said grain in the combustion chamber of a rocket motor conventionally provided with a restricted nozzle and a Suitable means for igniting said grain. After ignition of the grain, the burning surface generates in a direction normal to the initial ignition surface through successive, prescheduled zones of different elec-tron and ion-emissive capacity to produce a high temperature, high pressure gas stream of varying electron and ion density, which vents out the nozzle of the motor.

We have further discovered that additional controlled modulation of emitted electron and ion density produced in the aforedescribed manner can be achieved by controlled injection of a liquid into the combustion gases. The injected liquid modulates by its cooling effect on the combustion products which, in turn, increases the rate of ion and electron recombination, and thereby reduces their density to the degree required for a particular application. Certain liquids, such as Water and halogenated organic compounds, in addition to the cooling produced by their change to gaseous state, also ionize at the high temperature to produce anions such as hydroxyl, chloride, bromide or iiuoride ions, which combine With the free electrons in the gas stream and fur-ther reduce their intensity. The liquid can be injected into the combustion chamber rearwardly of the grain or into the nozzle at any point, including its convergent, throat, and divergent zones.

The electron and ion emissive compositions employed to make the shaped grain of the invention basically comprise a mixture of an alkali metal, inorganic oxidizer salt, such as the nitrate, chlorate, perchlora-te, sulfate, chromate and dichromate salts of lithium, sodium, potassium, rubidium and cesium, and mixtures thereof, and a inelydivided metal of lower oxidation potential than that of the alkali metal component of the particular oxidizer salt. Suitable metals include, for example, aluminum, magnesiurn, iron, manganese, zinc, cadmium, cobalt and nickel. In general, the preferred alkali metal is cesium because of its high degree of ioniza-tion; the preferred salts are the nitrates and perchlorates because of their gasgenerating properties and stability, and the preferred exothermically reactive metals are aluminum, magnesium and iron. Upon ignition, the aforedescribed components react exothermically to produce an oxide of the finelydivided free metal, the alkali metal in the form of its free, monovalent cation, free electrons, and other products determined by the other constituents of the oxidizer salt employed. The relative proportions of alkali metal oxidizer salt and finely-divided reactive metal are not critical since they will be varied according to the desired ernissivity. It is essential only that the oxidizer salt be present in amount sufficient to support lactive combustion of the metal.

Within the con-text of the aforedescribed reactive mixture of alkali metal oxidizer salt and timely-divided other metal, the rate of electron emission can be Varied in a number of Ways as, for example:

(l) By varying the proportion of the same oxidizer and metal components.

(2) By employing the same alkali metal oxidizer salt With different reactive metals or mixtures of metals.

(3) By employing diiferent oxidizer salts or mixtures of oxidizer salts With the same metals. The oxidizer salt can vary in its alkali metal cation component or in the anion component.

(4) By addition of modifying components to the aforedescribed reactive mixture Which:

(a) Enter into the oxidation reaction, such as oxidizers other than alkali metal oxidizer salts, e.g. ammonium chlorate, perchlorate, nitrate, ehromate, or dichromate; lead peroxide, sodium peroxide, and the like.

(b) Decompose to produce diluting gases such as sodiurn azide, cesium azide, lithium carbonate, calcium carbonate, azo-bis-isobutyronitrile, diazoaminobenzene, 1,1- azo-bis (formarnide), N,N dinitroso pentamethylene tetramine, dinitroso terephthalamide, benzene sulfonyl hydrazide, and the like.

(c) Foster recombination of the emitted cations and electrons, such as organic compounds, preferably polymers, which have the additional important advantage of acting as binders for the alkali metal oxidizer salt and timely-divided metal reaction components, and producing gases.

The organic diluent can be any suitable organic compound or mixture of organic compounds. It can be inert, the -term inert as used herein meaning a compound Which requires an external source of oxygen, such as a solid, inorganic oxidizer for combustion. Illustrative of suitable organic compositions are the various solid polymeric binders, such as polyether polysuldes, polynrethanes, butadiene-acrylic acid and -methacrylic acid copolymers cross-linked with an epoxy, alkyd polyesters, polyamides, cellulose esters, e.g. cellulose acetate, cellulose ethers, e.g. ethyl cellulose, polyvinyl chloride, asphalt, and the like.

Many of the solid polymeric binders preferably include high-boiling, organic, liquid plasticizers to improve physical properties and processing of the propellant composition. Any of the numerous organic plasticizers known in the art and compatible with the propellant composition can be employed. Illustra-tive examples of sui-table organic plasticizers include sebacates such as dibutyl sebacate and dioctyl sebacate; phthalates such as dibutyl phthalate and dioctyl phthalate; adipates such as dioctyl adiptate; glycol esters of higher fatty acids, and the like.

The organic diluent binder can also comprise an active organic compound, a mixture of such compounds, or a mixture of such a compound with an inert organic compound, such as an inert organic plasticizer, the term active compound as employed herein meaning a compound which .contains molecularly ycombined oxygen available vfor combustion of "other components of the molecule, such as carbon. Examples of active organic fuel cornpounds include th-ose containing nitroso, nitro, nit-rite, and nitrate radicals, such as cellulose nitrate 4and nitroglycerine.

(5) By modifying the compositi-ons to vary the burning rate as by:

(a) Addition of a burning rate catalyst such as copper and other metal or ammonium chromites and chromates, rnetal oxides, e.g. chromium sesquiox-ide, ferric oxide, ferrie ferrocyanide, and .the like. Such catalysts are particularly effective in compositions containing also an organic polymer modiiier.

-(b) Variation in oxidizer salt and finely-divided metal particle size.

It will be obvious that the amount of the various aforedescribed modifiers added to the alkali metal oxidizer saltreactive metal mixture, although generally in minor proportion, will be determined by that required to produce the desired degree of emissivity. This can readily be determined both by preliminary calculation land routine testing.

Although the emitted alkali metal cations are in gaseous state at the high combustion reaction temperatures, .thereby producing some elevated pressure in the rocket combustion chamber, it is generally desirable in order to :ensure reliable and rapid burning, that another gasifying component be present. This can be accomplished by the presence of a gas producing element such as nitrogen or chlonine in .the anion of the alkali metal oxidizer salt, as @shown `for example by the following equations:

Thus, where a non-gasifying oxidizer salt is used, such as a chromate or dichromate, it is preferable to use it in admixture with a gas-forming oxidizer salt, such as a nitrate or perchlorate, or with a modifier, such as an organic binder, which is either oxidized to produce gases suc-h as CO2, CO, H2 or H2O or decomposes under the heat of reaction into gaseous products, or an inorganic modifier such as an azide or carbonate which decomposes to form gases.

`ln practicing the invention, the desired progression of electron and ion emission density is rst determined for the particular application. The particular compositions modified as aforedescribed to provide the desired different levels of emission are selected and formulated with the aid of routine tests to determine emissivity` One such test, for example, can be made by fabricating small test generators, using the Imaterial proposed for each increment as a solid, non-incremental grain, and firing each of these in an environment similar to that proposed for the operation of the nal unit. lElectron generation rates can then be measured by suitable conventional micro-wave apparatus, thus confirming calculated electron generati-on rates.

The preselected compositions can be molded separately into the required size and shape, e.g. discs of preselected thickness, and then cemented together in the pre-scheduled order to produce the finished grain of incrementally varying emissivity. The molding can be accomplished in a variety of conventional ways. For example, the mixture of alkali metal oxidizer salt .and finely-divided metals, with or without additional ingredients to modify emissivity, can be pressure molded. If a polymeric binder is used, conventional methods for processing composite propellants can be applied. Any suitable cement or adhesive can be employed to bond the layers or increments together, such `as epoxy, epoxy-polyamide, and polyurethane adhesives, inorganic cements, such as phosphate-bonded zirconium oxide cements and the like. A mixture of the alkali metal oxidizer salt and nely-divided metal reactants, preferably in relatively low concentration, can be introduced into the adhesive formulation to minimize sharp demarcations in emission rate and to facilitate continued generation of burning surface from one composition zone to the next.

`In some cases, it may be advisable to superimpose laye-rs -of the different composition mixtures in powder form in :a mold and to consolidate the entire grain by applying high pressures, eg. up to 150,000 p.s.i. This method has the advantages of fabricating the entire incrementally constructed grain in a single pressure molding step and minimizing sharp changes in emission rate between charge increments because of composition interdiffus-ion at the different composition layer interfaces.

The grain can be fabricated of any number of desired composition increments of any suitable thickness to provide any desired emission progressivity or regressivity determined by the particular application. The shape of the grain can also be varied as desired. It can, for example, be a conventional, cylindrical end-burning grain which is inhibited against combustion except for a single end surface, as shown in FlGURE 1. lt can also be designed as an internal burning grain suitably perforated as, for example, lwith a star-shaped perforation, or a perforated interior-exterior burning grain, with the composition increments of different emissivity superimposed in essentially annular layers.

The combustible, gas-generating grain need not be entirely composed of serially disposed segments :of different electron and ion emissivity. It is essential only that at least a portion of the grain be thus serially segmented in the direction of ame propagation. A cylindrical, endburning gra-in, for example, can be fabricated having embedded therein a longitudinal, axial, seri-ally segmented core, with the remainder or annular portion of the grain composed of an essentially uniform gas-generating propellant composition which may or may not, as desired, be electron emissive. This annular zone can, for example, be any conventional gas-generating propellant, such as double-'base or a composite comprising an organic polymerio fuel binder, e.g. polyvinyl chloride, polyurethane, alkyd polyester, cellulose ester (e.g. cellulose acetate), cellulose ether (e.g. ethyl cellulose), polyamide, polyether, polysulfide and the like .and a suitable inorganic oxidizer, e.g. ammonium perchlorate, ammonium nitrate, lead peroxide and the like. Preferably, however, it is also electron-generating, namely composed of a mixture of alkali-metal `oxidizer salt and exothermically reactive metal` After ignition of a grain constructed in such manner, the serially segmented core provides the desired, prescheduled rate of electron and ion emissivity.

Referring now to the drawings, FGURE 1 shows a conventionally designed rocket motor comprising combustion chamber l suitably lined with insulation 2 fitted with restricted convergent-divergent nozzle 3 and igniter 4. Propellant grain 5 is a cylindrical end-burning grain having an exposed initial ignition surface 6 and inhibited on its other surfaces by restrictive liner 7. Grain 5 is built of a plurality of segments 5a, Sb, 5c, 5d, 5e, 5f and 5g cemented together with suitable adhesive, as aforedescribed, each composed of a consolidated mixture of an alkali metal oxidizer salt and a finely-divided reactive metal suitably compounded to produce, upon ignition, a different rate of electron and ion emission. After ignition of the initial burning surface 6, the burning surface regenerates longitudinally along 4the grain with resulting serial combustion of each of the discs and concomitant preselected change in electron and ion emission.

Example 1 The following compositions of different emissivity illu-strate how variation in concentration and additives can be employed to fabricate incremental grains of the desired variation in electron and ion production:

78.32% cesium nitrate-{-21.68% aluminum. Combustion at 121 p.s.i.a.; exhaust expanded to 14.7 p.s.i.a. Percent electrons in gas- 2.30 mole percent. Exhaust temperature--3573 K.

67.65% cesium nitrate[-20.35% aluminnm-l-l2% double base (50% nitrocellulose, 35% nitroglycerine and dibutyl phthalate). Combustion at 121 p.s.i.a.; exhaust expanded to 14.7 p.s.i.a. Percent electrons in gas-0.334 mole percent. Exhaust temperature- 3290 K.

III.

63.42% cesium nitrate-l-19.82% aluminum-146.75% double base (50% nitrocellulose, 35% nitroglycerine and 15% dibutyl phthalate). Combustion at 121 p.s.i.a.; exhaust expanded to 14.7 p.s.i.a Percent electrons in gas-0.218 mole percent. Exhaust temperature-3l54 K.

60.53% cesium nitrate+19.46% aluminum-l-% double base (50% nitrocellulose, 35% nitroglycerine and 15% dibutyl phthalate). Combustion at 121 p.s.i.a.; exhaust expanded to 14.7 p.s.i.a. Percent electrons in gas-0167 mole percent. Exhaust temperature- 3068 K.

76.35% cesium perchlorate and 23.65% aluminum mixture. Combustion at 121 p.s.i.a.; exhaust expanded to 14.7 p.s.i.a. Percent electrons in gas- 0.819 mole per cent. Exhaust temperature-3804" K.

Example 2 The following compositions of different electron and ion emissivity were prepared and tested for ignitibility and burning rate:

Cesium nitrate percent 78.32 Aluminum do 21.68 Molding pressure p.`s.i 50,000 B,-R.1000 in./sec 0.20

Cesium perchlorate percent 76.4 Aluminum do 23.6 Molding pressure p.s.i 40,000 B.R.600 in./sec 1.81

Cesium perchlorate percent 70 Aluminum do '3 0 Molding pressure p.s.i 40,000 B.R.5g{) .IIL/SEC..-

Cesium nitrate percent 78.32 Aluminum do 10.84 Magnesium do 10.84 Molding pressure p.s.i 30,000 B.R.100q I1'1./SBC V.

Potassium nitrate percent 65.32 Aluminum do 34.80 Molding pressure p.s.i. 20,000 B.`R10g0 -..IIL/Sec-..

An additional increment of control can be achieved, as aforedescribed, by injection of a liquid into the stream of combustion products as shown in FIGURE 1. The liquid can be any liquid vaporizable into gaseous state at the temperature of the combustion gases and includes, for example, water, halogenated hydrocarbons, such as ethylene dichloride, the liquid Freons, c g. trichloromonouoromethane, dischlorodifluoromethane, dichlorotetraiiuoromethane; dioxane, toluene, and the like. The liquid preferably is water because of its high heat of vaporization and formation of negatively charged hydroxyl ions. The liquid is supplied from a suitable storage container (not shown) through valve 8, the opening and closing of which can be controlled in any suitable manner, as by motor 9 which can be remotely controlled if desired. The liquid passes through tube 10 into annulus 11 surrounding the nozzle and is injected in this case into the venting gases through four apertures 12. Liquid injection can be continuous to compensate for a preprogrammed grain to be used under somewhat altered conditions. More generally, it will be discontinuous, intermittent or pulsating -to reproduce pulsating, ionized atmospheric phenomena which are sometimes encountered as, for example, in the region of the Aurora Borealis.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention can be embodied in other forms but within the scope ofthe claims.

We claim:

1. A shaped combustible grain having at least one initial ignition surface and comprising a plurality of adjacent bonded segments of gas-generating composition arranged in a direction normal to said initial ignition surface, each of said segments consisting essentially of a mixture of cesium oxidizer salt and finely-divided reactive metal exothermically reactive with said salt to produce free electrons and free alkali metal cations, said salt being present in an amount suicient to maintain active combustion of said metal, the composition of said segments being varied to produce electrons land cations at a difierent rate from that of the next adjacent segment during combustion, whereby said rate of electron and ion emission can be modulated in a preselected manner.

2. The grain according to claim 1 wherein the segments are arranged serially in a direction normal to said initial ignition surface.

3. The grain according to claim 1 wherein the cesium oxidizer salt is cesium nitrate and the finely-divided reactive metal is aluminum.

4. A generator device for producing a high-temperature, high-pressure ionized gas stream containing electrons and ions in modulated emission density, comprising a combustion chamber, a shaped grain as defined in claim 1 seated in said combustion chamber and means for igniting said grain.

5. A generator device for producing a high-temperature, high-pressure ionized gas stream containing electrons and ions in modulated emission density, comprising a combustion chamber, a shaped grain as defined in claim 1 seated in said combustion chamber, and means for igniting said grain.

6. The gas generator device of claim 5 which includes means for 4injecting a vaporizable liquid into the combustion gases at a point rearward of said combustible grain.

7. The grain according to claim 1 wherein the cesium oxidizer salt is selected from the group consisting of cesium nitrate and cesium perchlorate, and the finelydivided reactive metal is selected from the group consisting of aluminum, magnesium, and iron.

8. A generator device for producing a high-temperature, high pressure ionized gas stream containing electrons and ions in modulated emission density, comprising a combustion chamber, a shaped grain as delined in claim 7 seated in said combustion chamber, and means for igniting said grain.

9. The gas generator device of claim 8 which includes means for injecting a vaporizable liquid into the combustion gases at a point rearward of said combustible grain.

10. The gas generator device of claim 9 in which said liquid is Water.

11. The grain of claim 7 in which the composition of at least one of said segments contains in addition a minor amount of an agent eiective to modify the rate of said electron and ion emission.

12. The grain of claim 11 in which t'ne modifying agent is an organic polymer.

13. The grain of claim 11 in which the modifying agent is a burning rate catalyst.

14. The grain of claim 11 in which the modifying agent is a compound decomposable by heat to produce a gas.

References Cited by the Examiner UNITED STATES PATENTS 2,247,111 6/41 Batchelor et al. v50-35.6 2,522,113 9/50 Goddard 60-35.6 2,544,422 3/51 Goddard 60-35.6

S 1/61 Higgins et al. 149-42 2/61 Fox 149-42 4/61 Mahon et al 102-98 4/61 Boyer 149-37 8/61 Bice 149-42 5/62 Fox oil-35.6 8/ 62 Hutchinson 60-35.6

8/62 Baldwin 313-63 9/62 Kirkbride 60-35.6 2/64 Coates et al. 149-42 FOREIGN PATENTS 8/53 Great Britain.

15 MARK NEWMAN, Primm-y Examiner.

SAMUEL LEX/INE, CARLTON n. cRoYLE,

Examiners. 

1. A SHAPED COMBUSTIBLE GRAIN HAVING AT LEAST ONE INITIAL IGNITION SURFACE AND COMPRISING A PLURALITY OF ADJACENT BONDED SEGMENTS OF GAS-GENERATING COMPOSITION ARRANGED IN A DIRECTION NORMAL TO SAID INITITAL IGNITION SURFACE, EACH OF SAID SEGMENTS CONSISTING ESSENTIALLY OF A MIXTURE OF CESIUM OXIDIZER SALT AND FINELY-DIVIDED REACTIVE METAL EXOTHERMICALLY REACTIVE WITH SAID SALT TO PRODUCE FREE ELECTRONS AND FREE ALKALI METAL CATIONS, SAID SALT BEING PRESENT IN AN AMOUNT SUFFICIENT TO MAINTAIN ACTIVE COMBUSTION OF SAID METAL, THE COMPOSITION OF SAID SEGMENTS BEING VARIED TO PRODUCE ELECTRONS AND CATIONS AT A DIFFERENT RATE FROM THAT OF THE NEXT ADJACENT SEGMENT DURING COMBUSTION, WHEREBY SAID RATE OF ELECTRON AND ION EMISSION CAN BE MODULATED IN A PRESELECTED MANNER.
 4. A GENERATOR DEVICE FOR PRODUCING A HIGH-TEMPERATURE, HIGH-PRESSURE IONIZED GAS STREAM CONTAINING ELECTRONS AND IONS IN MODULATED EMISSION DENSITY, COMPRISING A COMBUSTION CHAMBER, A SHAPED GRAIN AS DEFINED IN CLAIM 1 AND IN SAID COMBUSTION CHAMBER AND MEANS FOR IGNITING SAID GRAIN. 